An increasing number of analytical techniques have been applied to the field of forensic trace evidence analysis in recent years (Brettell et al., “Forensic Science,” Analytical Chemistry 81(12):4695-4711 (2009)). New techniques and instrumentation are adapted to the discipline in order to increase the accuracy and efficiency of investigations. The science of “forensic ballistics” is designed to match a suspect to a shooting crime, and is vital to ensuring public safety. According to the Center for Disease Control, firearm related shootings were responsible for over 68% of homicides and were one of the three leading causes of injury related deaths in the United States in 2007 (Jiaquan et al., “Deaths: Final Data for 2007,” National Vital Statistics Reports 58(19) (2007)). The success of ballistic investigations must act as a deterrent to reduce the number of firearm related crimes in the United States. Matching a suspect to a crime often requires the recovery of some sort of physical evidence, whether it is the projectile (bullet), cartridge case or the actual firearm. Gunshot residue (GSR), or firearm discharge residue (FDR), recovered from several locations around the crime scene, is often utilized not only as physical but chemical evidence.
When a firearm is discharged, a mixture of chemicals is expelled from the barrel and deposited upon both the shooter's hand and around the impact site. This mixture of chemicals includes primers, accelerants, trace metals, and other particles which constitute the gunshot residue (GSR). GSR is not only created as a cloud in the direct vicinity of the gun, but GSR is also propelled in the wake of the bullet in the direction of the target. GSR is obtained from every shooting incident and needs to be analyzed. GSR plays an important role in forensic science in helping to determine certain factors of a shooting and related criminal case.
Gunshot residue (GSR) is caused by the combustion involved in the firing of ammunition. When a gun is fired, the trigger of the gun is pulled causing a firing pin to strike the ammunition (i.e., bullet), crushing the primer. The energy transfer causes explosion of the gun powder sending the bullet through the barrel. The velocity of the bullet is stabilized by a spiraling motion caused by lands and grooves in the barrel called riflings. In a crime laboratory, the riflings are often used to match a bullet to a particular gun provided the bullet-shell is found at the crime scene.
Matching a bullet to the weapon that fired it is a common forensic procedure. The bullet can be matched based upon its impressions caused by the riffling of the barrel, which differs from weapon to weapon. Chemical components of ammunitions also vary between type and size of calibers. Details of the bullet case, propellant, and primer depend upon the manufacturer and the source of ammunition (Romolo and Margot, “Identification of Gunshot Residue: A Critical Review,” Forensic Science International 119:195-211 (2001)). Generally, for hand guns the larger the caliber the more GSR will be expelled and deposited on the firer's hand (Meng and Caddy, “Gunshot Residue Analysis—A Review,” J. Forensic Sciences 42(4):553-570 (1997)). An on-site (crime scene) technique that rapidly identifies the type of caliber through analysis of the GSR would be an invaluable tool for a forensic investigator.
The chemical nature of GSR particles gives information about the gun, ammunition, and the shooting distance (and direction). GSR recovered at crime scenes is among the most important type of evidence to forensic investigators (Stich et al., “Raman Microscopic Identification of Gunshot Residues,” J. Raman Spectroscopy 29(9):787-790 (1998)). The chemical composition of GSR is directly related to the chemical composition of the ammunition used. In addition, the chemical composition of GSR varies with the type of weapon since the latter determines specific conditions of the combustion process. Therefore, differences from ammunition to ammunition and, between different firearms will propagate to differences in the GSR. Conventional methods of GSR identification use labor-intensive, technologically diverse methods that are costly in terms of time and sample usage (Stich et al., “Raman Microscopic Identification of Gunshot Residues,” J. Raman Spectroscopy 29(9):787-790 (1998)).
The objectives of any crime scene investigation are to preserve physical evidence and collect only valuable evidence for the analytical examination. The ability to characterize an unknown GSR at the scene of the crime without destruction or having to wait for laboratory results is, therefore a very critical step in crime scene investigation. GSR is often collected as forensic evidence to determine if a suspect has recently fired a weapon (Silva et al., “Gunshot Residues: Screening Analysis by Laser-Induced Breakdown Spectroscopy,” J. Brazilian Chem. Soc. 20(10):1887-1894 (2009); Romolo and Margot, “Identification of Gunshot Residue: A Critical Review,” Forensic Sci. Int'l., 119:195-211 (2001); Garofano et al., “Gunshot Residue—Further Studies on Particles of Environmental and Occupational Origin,” Forensic Sci. Int'l. 103(1):1-21 (1999); and Dockery and Goode, “Laser-Induced Breakdown Spectroscopy for the Detection of Gunshot Residues on the Hands of a Shooter,” Applied Optics 42(30):6153-6158 (2003)), estimate the shooting distance (Santos et al., “Firing Distance Estimation Through the Analysis of the Gunshot Residue Deposit Pattern Around the Bullet Entrance Hole by Inductively Coupled Plasma-Mass Spectrometry—An Experimental Study,” Am. J. Forensic Med. Pathol. 28(1):24-30 (2007); Capannesi et al., “Determination of Firing Distance and Firing Angle by Neutron Activation Analysis in a Case Involving Gunshot Wounds,” Forensic Sci. Int'l. 61(2-3):75-84 (1993); Sharma and Lahiri, “A Preliminary Investigation Into the Use of FTIR Microscopy as a Probe for the Identification of Bullet Entrance Holes and the Distance of Firing,” Science & Justice 49(3):197-204 (2009); Neri et al., “The Determination of Firing Distance Applying a Microscopic Quantitative Method and Confocal Laser Scanning Microscopy for Detection of Gunshot Residue Particles,” Int'l. J. Legal Med. 121(4):287-292 (2007); and Brown et al., “Image Analysis of Gunshot Residue on Entry Wounds: II—A Statistical Estimation of Firing Range,” Forensic Sci. Int'l. 100(3):179-186 (1999)) and confirm if a shooting has actually occurred.
Current methods for identifying GSR include the Modified Griess test, sodium rhodizionate test, gas-chromatography mass-spectrometry and scanning electron microscopy (SEM) combined with energy-dispersive X-ray analysis (EDX). Several of these methods require treating gunshot residue samples with reagents, including acids or other solvents, causing the methods to be destructive to the residue or other physical evidence involved with the sample. SEM/EDX is the preferred confirmatory test associated with GSR analysis (Stich et al., “Raman Microscopic Identification of Gunshot Residues,” J. Raman Spectroscopy 29(9):787-790 (1998)). Unfortunately, this test requires relatively excessive amounts of time due to sampling procedures. Additionally, with the use of “lead-free” or “nontoxic” ammunitions, it is difficult to prevent false positives when searching for GSR by conventional SEM/EDX protocols (Burleson et al., “Forensic Analysis of a Single Particle of Partially Burnt Gunpowder by Solid Phase Micro-Extraction-Gas Chromatography-Nitrogen Phosphorus Detector,” J. Chromatography A 1216(22):4679-4683 (2009)). Nevertheless, all of these methods test for the presence of GSR; but cannot identify and distinguish the type of caliber which produced the GSR recovered from the crime scene.
One conventional test for analyzing GSR is a chemical test, called the Modified Griess test. The Modified Griess test is a test to detect the presence of nitrite residues, and is the primary test used by firearms examiners to determine a muzzle-to-garment distance. The Modified Griess test is performed first on the GSR since the test will not interfere with later tests for lead residues. Nitrite residues are a byproduct of the combustion of smokeless gunpowder. When a gun is discharged, nitrite particles are expelled from the muzzle of a gun and can be imbedded in, or deposited on, the surface of a target. Another conventional test conducted on GSR is called the sodium rhodizionate test, which is a chemical test designed to determine if lead residues are present on the exhibit.
A problem with both the Modified Griess test and the sodium rhodizionate test is that most shooting cases involve firing at close range, and these tests are not applicable to shootings at close ranges (e.g., less than 5 feet). These techniques can only observe microscopic particles (particles whose diameter is a few microns or more) that are formed at distances of 5 feet or longer from the gun. Currently the GSR patterns are experimentally matched with the patterns at the crime scene on test firing. This is a time consuming and expensive process, and, again, does not work for short distances since it is difficult to observe a pattern in such a short distance. Moreover, these techniques require substantial amounts of GSR samples, which are difficult to obtain and are frequently contaminated. Accordingly, conventional techniques used for GSR analysis are limited, so prosecuting and defense attorneys typically rely on other evidence such as cartridge case volume and witness testimony to build a given case.
Several other analytical methods, including bulk and single particle analysis, are used to achieve GSR identification, but there is no standardized procedure to test for GSR. Single particle analysis combines chemical and morphological information to classify a suspected particle. The most widely accepted GSR analysis method is Scanning Electron Microscopy combined with Energy Dispersive X-Ray Spectroscopy (SEM/EDX). SEM/EDX is able to identify a sample as GSR based upon its ability to detect the elements mentioned previously in certain concentrations (Nesbitt et al., “Detection of Gunshot Residue by Use of the Scanning Electron Microscope,” J. Forensic Sci. 21:595-610 (1976)). Unfortunately, this test is excessive in terms of time, sampling procedures, and instrumentation requirements. Since this technique relies heavily on the detection of lead, the removal of lead containing primers by manufacturers, citing health reasons, (Steffen et al., “Chemometric Classification of Gunshot Residues Based on Energy Dispersive X-ray Microanalysis and Inductively Coupled Plasma Analysis With Mass-Spectrometric Detection,” Spectrochimica Acta Part B-Atomic Spectroscopy 62(9):1028-1036 (2007)) has caused an increase in false positive results for SEM/EDX procedures (Burleson et al., “Forensic Analysis of a Single Particle of Partially Burnt Gunpowder by Solid Phase Micro-Extraction-Gas Chromatography-Nitrogen Phosphorus Detector,” J. Chromatog. A 1216(22):4679-4683 (2009)). Furthermore, SEM/EDX is unable to detect lighter elements (oxygen, carbon, and nitrogen) found in components of the primer and propellant (Schwoeble and Exline, Current Methods in Forensic Gunshot Residue Analysis. CRC Press:New York (2000)) and consequently provides limited analysis. Nevertheless, elemental analysis techniques are used as identification rather than chemical characterization methods and are destructive to forensic evidence.
Bulk methods are based upon qualitative detection of specific elements, usually heavy metals. Combinations of lead (Pb), barium (Ba), and antimony (Sb) are considered unique to GSR (Schwoeble and Exline, Current Methods in Forensic Gunshot Residue Analysis. CRC Press:New York (2000)) but also occur in environmental contaminants. Unfortunately, bulk methods often make conclusions based upon detection of these elements that are not necessarily generated by GSR. This leads to a lack of specificity for methods such as flameless atomic absorption (FAA) and neutron activation analysis (NAA) (Wallace and McQuillan, “Discharge Residues from Cartridge-operated Industrial Tools,” J. Forensic Sci. Soc. 24(5):495-508 (1984)), which often misclassify environmental containments as being GSR.
Detection of these components provides several advantages over current elemental analysis techniques. For example, current techniques cannot distinguish whether detected lead originated from lead sulfate (a common primer component) or car battery acid. Therefore, the occupation of a suspect must be taken into account, because the source of the lead may not have originated from the discharging of a firearm. The method of the present invention offers a rapid, portable and sensitive alternative for GSR identification. Additionally, this technique will provide information about the original shooting parameters that can help link a suspect to a crime scene.
No existing technique is currently used to determine the type of ammunition and/or weapon type based upon GSR composition analysis. The forensic science community is in need of a technology that can (i) quickly identify the presence of GSR and (ii) match it to a specific type of ammunition and/or weapon type. The methods described in the present invention will fulfill these needs. The main advantage of the purposed technology over current GSR composition analysis is the ability to use the information to link the GSR to a specific ammunition and/or weapon type. Other advantages include the capacity to perform this technique in the field and in a relatively swift manner. Spectral collection at the crime scene and data analysis will be automated and will take very little time.
Accordingly, the present invention is directed to overcoming these deficiencies in the art.